2016-2019 BMW 7 Series Coolant Overflow Tank 17138610658

Also known as

Expansion Tank

Coolant Reservoir

Recovery Tank

Radiator Overflow Bottle

Header Tank

Surge Tank

Degas Bottle

What this part does

The coolant expansion tank stores excess engine coolant as it expands from engine heat and allows it to return to the radiator as the system cools down. It maintains the correct hydrostatic pressure in the primary high-temperature cooling circuit and houses the electronic coolant level sensor. Positioned in the upper engine bay, it serves as the primary fill and bleed point for the main cooling system. Over time, the plastic housing is subject to severe heat cycling, causing stress cracks along the factory welded seams. When the tank fails, it leads to slow coolant loss, a drop in system pressure, and potential engine overheating. A failing internal float will also permanently trigger a low coolant message on the iDrive display even when the fluid level is completely full.

Fits these vehicles

OEM and interchange numbers

17138610658

17 13 8 610 658

17-13-8-610-658

Before you order

Confirm whether your original reservoir pressure cap is functioning correctly, as a failing cap often mimics a cracked tank by venting coolant prematurely. This assembly contains the internal coolant level float; inspect your vehicle's wiring harness connector for green copper corrosion before attaching it to the replacement tank. After installing the tank, the cooling system must be bled using the automated electronic water pump bleeding procedure to prevent air pockets from forming in the cylinder heads or heater core. Verify your exact original part number against 17138610658, as the vehicle it came from features multiple cooling circuits, and the tank for the secondary intercooler circuit is visually similar but not interchangeable.